ok, then you have two options here which I will list out. As this is security, there is no simple solution, but any of these two options will work, it will just depend on how comfortable you feel doing them.
1)Reinstall the computer. This means you reinstall windows but lose all your data on the computer. It is not ideal, but the easiest way to do this. For this option, on the log in screen, hold down the SHIFT button and with it held down, click the power icon and choose restart. Keep SHIFT held until it has restarted into a menu. Choose Troubleshoot, then Reset my PC. This returns the PC to new, so you can set it up again.
2) Take it to a computer store, have them take out the hard drive and copy out your data to another disk. Then the reinstall can be done and you wont lose your data. Programs you have to install again.
If its new, do the first option then
Let me know the results please.